1. Field of Invention
The present invention relates generally to a method of controlling Hierarchical Mobile IPv6 (HMIPv6) network-based handover, and an Access Router (AR) and Mobile Node (MN) therefor, and, more particularly, to a handover method based on a network using HMIPv6 in an IEEE 802.16e network.
2. Description of Related Art
With the continuous development and diversification of wireless access technology, users desire to receive network service even in a mobile environment. In order to provide seamless service, a handover technology in the network layer is required. Mobile IPv6 (MIPv6) is a protocol that is proposed by the Internet Engineering Task Force (IETF). The protocol provides a mobile management function in the network layer.
In MIPv6, a handover process can be divided into processes, such as a movement detection process, a Care-of-Address (CoA) configuration process and a Binding Update (BU) process. While handover is being performed through the processes, an MN is unable to transmit or receive data. This period of time is called handover delay time.
In order to reduce the handover delay time generated when a handover scheme proposed in the MIPv6 protocol is used, the IETF proposed Fast MIPv6 (FMIPv6) and HMIPv6, which are based on MIPv6.
Of them, HMIPv6 differs from general MIPv6 as follows. During the handover process of general MIPv6, an MN performs BU on a Home Agent (HA) and a Correspondent Node (CN).
HMIPv6 is configured such that an MN performs BU on a Mobility Anchor Point (MAP), unlike MIPv6. HMIPv6 can have an advantage in that it can reduce the handover delay time through this mechanism as compared with the general MIPv6. The operation of the general HMIPv6 is described below.
FIG. 1 is a diagram showing the configuration of a general HMIPv6 network.
As shown in FIG. 1, an HMIPv6 network may include an HA 10, a CN 20, a MAP 100, a plurality of ARs 201 and 202, a plurality of Base Stations (BSs) 300, and at least one MN 400.
The Previous Access Router (PAR) 201 of the ARs corresponds to an AR that has accessed a network layer before the MN 400 performs handover. The Next Access Router (NAR) 202 of the ARs corresponds to an AR that will access the network layer after the MN 400 performs handover.
The Serving Base Station (SBS) 301 of the BSs 300 corresponds to a BS which has accessed a data link layer before the MN 400 performs handover. The Target Base Station (TBS) 302 of the BSs 300 corresponds to a BS which will access the data link layer after the MN 400 performs handover.
Each of the HA 10 and the CN 20 maps the permanent IP address of the MN 400 to a CoA pertinent to the permanent IP address, and transmits packets to a network to which the MN 400 belongs.
A handover method in the HMIPv6 network including the elements is described below.
In the case where the MN 400 has moved and handover has to be performed, the MN 400 selectively performs two types of BU processes depending on the situation.
First, in the case where the MN 400 has moved between the domains of MAPs 100, the MN 400 performs global BU (or inter-MAP). Second, in the case where the MN 400 has moved within the domain of an MAP 100, the MN 400 performs local BU (intra-MAP).
In an HMIPv6 environment, the MN 400 has two types of CoAs which are called a Regional CoA (RCoA) and a Local CoA (LCoA). The RCoA is a temporary address commonly used within the domain of the MAP 100, and a process of notifying the MAP 100 and the CN 20 of the relationship between RCoAs corresponds to global BU. The LCoA corresponds to the same address as a CoA in the existing MIPv6. A process of notifying the MAP 100 of the relationship between the newly created LCoA and RCoA corresponds to the local BU.
If the MN 400 moves and enters the domain of a new MAP 100, the MN 400 reconfigures two types of RCoA and LCoA. Accordingly, the MN 400 performs both global BU and local BU.
However, in the case where the MN 400 performs handover within the domain of the MAP 100, the MN 400 performs a position registration procedure by performing a local BU process only on the MAP 100. Next, the MAP 100 operates like an HA in the domain that the MN 400 has accessed and performs position management of the MN 400. A method of the MN 400 performing handover within the domain of the MAP 100 is described in more detail.
FIG. 2 is a diagram showing a handover procedure within the domain of a MAP in HMIPv6 over an IEEE 802.16e network.
Referring to FIG. 2, when the MN 400 moves, it terminates a connection to the SBS 301 to which the MN 400 is connected and attempts to set up a new connection to the TBS 302.
The data link layer 402, that is, the MN Layer 2, of the MN 400 performs a handover process from the SBS 301 to the TBS 302 in the data link layer, through processes from a MOB_NBR-ADV transmission process 5201 to a DSA-ACK transmission process S206 in accordance with the IEEE 802.16e standard. This handover in the data link layer is also referred to as Layer 2 or L2 handover.
After the handover in the data link layer or L2 handover is completed, the network layer 401, that is, the MN Layer 3, of the MN 400 starts handover in the network layer by receiving a router advertisement message at step S207, including information of MAP 100, from the NAR 202. The handover in the network layer is also referred to as Layer 3 or L3 handover.
The network layer of the MN can acquire the global IP address and network prefix of the MAP 100 from the router advertisement message received at step S207. The MN 400 can determine whether it performs handover within the domain of a MAP 100 or performs handover between the domains of MAPs 100, or handover in the network layer is not necessary based on the global IP address and network prefix of the MAP 100.
In the case where handover in the network layer is not necessary, the MN 400 has only to maintain a current LCoA and RCoA configuration, so that a detailed description thereof is omitted here.
The L3 layer 401 of the MN 400 creates an LCoA based on the network prefix of the NAR 202 which can be acquired from the router advertisement message received at step S207.
In the case where global BU is necessary, the MN 400 creates an RCoA based on the network prefix of the MAP 100. Here, an IPv6 stateless address auto configuration may be used.
In FIG. 2, the case where global BU is not necessary and only local BU is necessary is assumed. This assumption corresponds to the case where the MN 400 performs handover within the domain of the MAP 100. In this case, the network layer 401 of the MN 400 performs only local BU along with the MAP 100 at step S208.
After local BU is completed, the MAP 100 creates a tunnel between the network layer 401 of the MN 400 and the MAP 100. The MAP 100 then transmits packets, having the MN 400 as a destination, to the NAR 202 to which the MN 400 will belong through the tunnel using a binding cache at step S210. Finally, the NAR 202 transmits the packets, which have been received through the tunnel, to the MN 400 at step S211.
The time taken for the above-described handover (that is, the handover delay time) basically includes movement detection time, CoA configuration time, and BU time.
In general HMIPv6, in the case where handover is generated within the domain of the MAP 100, the time taken for the BU time, which belongs to the entire handover delay time, can be reduced, thereby reducing the entire handover delay time.
However, in general HMIPv6, handover in the L3 layer 401 of the MN 400 starts after handover in the L2 layer 402 has been terminated. In other words, handover in the network layer starts with the process 5207 of receiving the router advertisement message from a new AR (NAR). The network layer 401 of the MN 400 performs movement detection through the router advertisement message.
In this case, the time taken for the MN 400 to wait for the reception of the router advertisement message varies depending on a router advertisement message time interval set in the AR. Accordingly, after handover in the data link layer has been completed, the MN 400 may have to wait for a long time depending on the setting of the AR.
If handover delay is long as described above, the MN 400 inevitably experiences great packet loss. Although packet lossless is guaranteed in an upper layer using a mechanism, such as the Transmission Control Protocol (TCP), there is a problem in that a long handover delay time may lead to a low packet throughput in the MN 400 because of the characteristics of TCP.